U.S. patent application number 13/546436 was filed with the patent office on 2012-11-01 for nanopatterning method and apparatus.
This patent application is currently assigned to Rolith, Inc.. Invention is credited to Boris Kobrin.
Application Number | 20120274004 13/546436 |
Document ID | / |
Family ID | 47067294 |
Filed Date | 2012-11-01 |
United States Patent
Application |
20120274004 |
Kind Code |
A1 |
Kobrin; Boris |
November 1, 2012 |
NANOPATTERNING METHOD AND APPARATUS
Abstract
Embodiments of the invention relate to methods and apparatus
useful in the nanopatterning of large area substrates, where a
movable nanostructured film is used to image a radiation-sensitive
material. The nanopatterning technique makes use of Near-Field
photolithography, where the nanostructured film used to modulate
light intensity reaching radiation-sensitive layer. The Near-Field
photolithography may make use of an elastomeric phase-shifting
mask, or may employ surface plasmon technology, where a movable
film comprises metal nano holes or nanoparticles.
Inventors: |
Kobrin; Boris; (Dublin,
CA) |
Assignee: |
Rolith, Inc.
Pleasanton
CA
|
Family ID: |
47067294 |
Appl. No.: |
13/546436 |
Filed: |
July 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/US2011/000029 |
Jan 7, 2011 |
|
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13546436 |
|
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Current U.S.
Class: |
264/496 ;
425/174.4; 977/887 |
Current CPC
Class: |
G03F 1/34 20130101; G03F
1/60 20130101; G03F 1/50 20130101; B82Y 40/00 20130101; G03F 7/2014
20130101; G03F 7/0012 20130101; G03F 7/2032 20130101; G03F 7/2035
20130101 |
Class at
Publication: |
264/496 ;
425/174.4; 977/887 |
International
Class: |
B29C 59/16 20060101
B29C059/16 |
Claims
1. A method of nanopatterning comprising: a) providing a substrate
having a radiation-sensitive layer on said substrate surface; b)
providing a movable nanostructured film, c) contacting said
nanostructured film with said radiation-sensitive layer on said
substrate along a surface of contact; d) distributing radiation
through said contact, while translating said substrate against said
film.
2. A method in accordance with claim 1, wherein said nanostructured
film causes modulation of light intensity in the plane of
radiation-sensitive layer.
3. A method in accordance with claim 2, wherein said nanostructured
film has a surface relief.
4. A method in accordance with claim 3, wherein said nanostructured
film is a phase-shifting mask which causes radiation to form an
interference pattern in said radiation-sensitive layer.
5. A method in accordance with claim 2, wherein said nanostructured
film is made of conformable elastomeric material.
6. A method in accordance with claim 2, wherein said nanostructured
film is made of a more than one layer of transparent flexible
materials.
7. A method in accordance with claim 6, wherein the outer layer is
made of elastomeric material.
8. A method in accordance with claim 6, wherein the outer layer is
made of silane material.
9. A method in accordance with claim 3, wherein said surface relief
is fabricated by molding or casting from nanostructured master
substrate.
10. A method in accordance with claim 2, wherein said conformable
nanostructured film is a plasmonic mask.
11. A method according with claim 10, wherein said plasmonic mask
is made of metal film having arrays of nanoholes.
12. A method according with claim 10, wherein said plasmonic mask
is made of with nanopatterned metal layer, deposited or laminated
on transparent flexible film.
13. A method according with claim 10, wherein said plasmonic mask
is made by array of metal nanoparticles deposited on transparent
flexible film.
14. A method in accordance with claim 1, wherein said contacting
between nanostructured film and a radiation-sensitive layer is done
using movable arm.
15. A method in accordance with claim 14, wherein said movable arm
is removed from the contact during photosensitive layer
exposure.
16. A method in accordance with claim 14, wherein said movable arm
is a cylinder, and such cylinder is rotated while in contact with
the nanostructured film
17. A method in accordance with claim 16, wherein said cylinder has
flexible walls and is pressurized by a gas.
18. A method in accordance with claim 16, wherein a light source is
positioned inside such cylinder.
19. A method in accordance with claim 1, wherein said substrate is
translated in a direction toward or away from a contact line of
said nanostructured film during distribution of radiation from said
contact line.
20. A method in accordance with claim 1, wherein said
nanostructured film is moved in a closed loop.
21. A method in accordance with claim 1, wherein said
nanostructured film is translated from roll to roll.
22. A method in accordance with claim 1, wherein said substrate is
rigid plate.
23. A method in accordance with claim 1, wherein said substrate is
has a curvature.
24. A method in accordance with claim 1, wherein said substrate is
a flexible film.
25. A method in accordance with claim 1, wherein an additional
nanostructured flexible film and a light source are provided on the
other side of the substrate coated with photo-sensitive layer on
both surfaces for nanopatterning on both sides of the
substrate.
26. A method in accordance with claim 1, wherein said
radiation-sensitive layer is a UV-curable liquid resist.
27. An apparatus to carry out nanopatterning, comprising: a) a
nanostructured film and b) a radiation source which supplies
radiation of a wavelength of 650 nm or less through a portion of
said nanostructured film, while said portion is in contact with a
radiation-sensitive layer of material.
28. An apparatus in accordance with claim 27, wherein
nanostructured film is a polymer having surface relief.
29. An apparatus in accordance with claim 27, wherein
nanostructured film is a perforated metal film or polymer film with
metal nanoparticles.
30. An apparatus in accordance with claim 27, wherein said
nanostructured film has more than one layer.
31. An apparatus in accordance with claim 27, wherein a movable
cylinder is provided to control nanostructured film contact with
said radiation-sensitive layer.
32. An apparatus in accordance with claim 31, wherein such cylinder
is pressurized by a gas.
33. An apparatus in accordance with claim 27, wherein said
nanostructured film is configured to translate from roll to
roll.
34. An apparatus in accordance with claim 27, wherein said
nanostructured film is configured to move in a closed loop.
Description
CLAIM OF PRIORITY
[0001] The present application claims the priority benefit of
commonly assigned U.S. provisional Application No. 61/335,877,
filed Jan. 12, 2010 and this application is a continuation-in-part
of commonly-assigned, co-pending PCT application serial no.
PCT/US2011/000029, filed Jan. 7, 2011, the entire disclosures of
which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] Embodiments of the invention relate to nanopatterning
methods which can be used to pattern large substrates or substrates
such as films which may be sold as rolled goods. Other embodiments
of the invention pertain to apparatus which may be used to pattern
substrates, and which may be used to carry out method embodiments,
including the kind described.
BACKGROUND OF THE INVENTION
[0003] This section describes background subject matter related to
the disclosed embodiments of the present invention. There is no
intention, either express or implied, that the background art
discussed in this section legally constitutes prior art.
[0004] Nanostructuring is necessary for many present applications
and industries and for new technologies which are under
development. Improvements in efficiency can be achieved for current
applications in areas such as solar cells and LEDs, and in next
generation data storage devices, for example and not by way of
limitation.
[0005] Nanostructured substrates may be fabricated using techniques
such as e-beam direct writing, Deep UV lithography, nanosphere
lithography, nanoimprint lithography, near-filed phase shift
lithography, and plasmonic lithography, for example.
[0006] Nanoimprint Lithography (NIL) creates patterns by mechanical
deformation of an imprint resist, followed by subsequent
processing. The imprint resist is typically a monomeric or
polymeric formulation that is cured by heat or by UV light during
the imprinting. There are a number of variations of NIL. However,
two of the processes appear to be the most important. These are
Thermoplastic Nanoimprint Lithography (TNIL) and Step and Flash
Nanoimprint Lithography (SFIL).
[0007] TNIL is the earliest and most mature nanoimprint
lithography. In a standard TNIL process, a thin layer of imprint
resist (a thermoplastic polymer) is spin coated onto a sample
substrate. Then a mold, which has predefined topological patterns,
is brought into contact with the sample, and pressed against the
sample under a given pressure. When heated above the glass
transition temperature of the thermoplastic polymer, the pattern on
the mold is pressed into a thermoplastic polymer film melt. After
the sample, with impressed mold is cooled down, the mold is
separated from the sample and the imprint resist is left on the
sample substrate surface. The pattern does not pass through the
imprint resist; there is a residual thickness of unchanged
thermoplastic polymer film remaining on the sample substrate
surface. A pattern transfer process, such as reactive ion etching,
can be used to transfer the pattern in the resist to the underlying
substrate. The variation in the residual thickness of unaltered
thermoplastic polymer film presents a problem with respect to
uniformity and optimization of the etch process used to transfer
the pattern to the substrate.
[0008] Tapio Makela et al. of VTT, a technical research center in
Finland, have published information about a custom built laboratory
scale roll-to-roll imprinting tool dedicated to manufacturing of
submicron structures with high throughput. Hitachi and others have
developed a sheet or roll-to-roll prototype NIL machine, and have
demonstrated capability to process 15 meter long sheets. The goal
has been to create a continuous imprint process using belt molding
(nickel plated molds) to imprint polystyrene sheets for large
geometry applications such as membranes for fuel cells, batteries
and possibly displays.
[0009] Hua Tan et al of Princeton University have published 2
implementations of roller Nanoimprint lithography: rolling cylinder
mold on flat, solid substrate, and putting a flat mold directly on
a substrate and rolling a smooth roller on top of the mold. Both
methods are based on TNIL approach, where roller temperature is set
above the glass transition temperature, Tg, of the resist (PMMA),
while the platform is set to temperature below Tg. Currently the
prototype tools do not offer a desirable throughput. In addition,
there is a need to improve reliability and repeatability with
respect to the imprinted surface.
[0010] In the SFIL process, a UV curable liquid resist is applied
to the sample substrate and the mold is made of a transparent
substrate, such as fused silica. After the mold and the sample
substrate are pressed together, the resist is cured using UV light,
and becomes solid. After separation of the mold from the cured
resist material, a similar pattern to that used in TNIL may be used
to transfer the pattern to the underlying sample substrate.
Dae-Geun Choi from Korea Institute of Machinery suggested using
fluorinated organic-inorganic hybrid mold as a stamp for
Nanoimprint lithography, which does not require anti-stiction layer
for demolding it from the substrate materials.
[0011] Since Nanoimprint lithography is based on mechanical
deformation of resist, there are a number of challenges with both
the SFIL and TNIL processes, in static, step-and-repeat, or
roll-to-roll implementations. Those challenges include template
lifetime, throughput rate, imprint layer tolerances, and critical
dimension control during transfer of the pattern to the underlying
substrate. The residual, non-imprinted layer which remains after
the imprinting process requires an additional etch step prior to
the main pattern transfer etch. Defects can be produced by
incomplete filling of negative patterns and the shrinkage
phenomenon which often occurs with respect to polymeric materials.
Difference in thermal expansion coefficients between the mold and
the substrate cause lateral strain, and the strain is concentrated
at the corner of the pattern. The strain induces defects and causes
fracture defects at the base part of the pattern mold releasing
step.
[0012] Soft lithography is an alternative to Nanoimprint
lithography method of micro and nano fabrication. This technology
relates to replica molding of self assembling monolayers. In soft
lithography, an elastomeric stamp with patterned relief structures
on its surface is used to generate patterns and structures with
feature sizes ranging from 30 nm to 100 nm. The most promising soft
lithography technique is microcontact printing (.mu.CP) with
self-assembled monolayers (SAMS). The basic process of .mu.CP
includes: 1. A polydimethylsiloxane (PDMS) mold is dipped into a
solution of a specific material, where the specific material is
capable of forming a self-assembled monolayer (SAM). Such specific
materials may be referred to as an ink. The specific material
sticks to a protruding pattern on the PDMS master surface. 2. The
PDMS mold, with the material-coated surface facing downward, is
contacted with a surface of a metal-coated substrate such as gold
or silver, so that only the pattern on the PDMS mold surface
contacts the metal-coated substrate. 3. The specific material forms
a chemical bond with the metal, so that only the specific material
which is on the protruding pattern surface sill remains on the
metal-coated surface after removal of the PDMS mold. The specific
material forms a SAM on the metal-coated substrate which extends
above the metal-coated surface approximately one to two nanometers
(just like ink on a piece of paper). 4. The PDMS mold is removed
from the metal-coated surface of the substrate, leaving the
patterned SAM on the metal-coated surface.
[0013] Optical Lithography does not use mechanical deformation or
phase change of resist materials, like Nanoimprint lithography, and
does not have materials management problems like Soft Lithography,
thus providing better feature replication accuracy and more
manufacturable processing. Though regular optical lithography is
limited in resolution by diffraction effects some new optical
lithography techniques based on near field evanescent effects have
already demonstrated advantages in printing sub-100 nm structures,
though on small areas only. Near-field phase shift lithography
NFPSL involves exposure of a photoresist layer to ultraviolet (UV)
light that passes through an elastomeric phase mask while the mask
is in conformal contact with a photoresist. Bringing an elastomeric
phase mask into contact with a thin layer of photoresist causes the
photoresist to "wet" the surface of the contact surface of the
mask. Passing UV light through the mask while it is in contact with
the photoresist exposes the photoresist to the distribution of
light intensity that develops at the surface of the mask. In the
case of a mask with a depth of relief that is designed to modulate
the phase of the transmitted light by .pi., a local null in the
intensity appears at the step edge of relief. When a positive
photoresist is used, exposure through such a mask, followed by
development, yields a line of photoresist with a width equal to the
characteristic width of the null in intensity. For 365 nm (Near UV)
light in combination with a conventional photoresist, the width of
the null in intensity is approximately 100 nm. A PDMS mask can be
used to form a conformal, atomic scale contact with a flat, solid
layer of photoresist. This contact is established spontaneously
upon contact, without applied pressure. Generalized adhesion forces
guide this process and provide a simple and convenient method of
aligning the mask in angle and position in the direction normal to
the photoresist surface, to establish perfect contact. There is no
physical gap with respect to the photoresist. PDMS is transparent
to UV light with wavelengths greater than 300 nm. Passing light
from a mercury lamp (where the main spectral lines are at 355-365
nm) through the PDMS while it is in conformal contact with a layer
of photoresist exposes the photoresist to the intensity
distribution that forms at the mask.
[0014] Yasuhisa Inao, in a presentation entitled "Near-Field
Lithography as a prototype nano-fabrication tool", at the 32nd
International Conference on Micro and Nano Engineering in 2006,
described a step-and-repeat near-field nanolithography developed by
Canon, Inc. Near-field lithography (NFL) is used, where the
distance between a mask and the photoresist to which a pattern is
to be transferred are as close as possible. The initial distance
between the mask and a wafer substrate was set at about 50 .mu.m.
The patterning technique was described as a "tri-layer resist
process", using a very thin photoresist. A pattern transfer mask
was attached to the bottom of a pressure vessel and pressurized to
accomplish a "perfect physical contact" between the mask and a
wafer surface. The mask was "deformed to fit to the wafer". The
initial 50 .mu.m distance between the mask and the wafer is said to
allows movement of the mask to another position for exposure and
patterning of areas more than 5 mm.times.5 mm. The patterning
system made use of i-line (365 nm) radiation from a mercury lamp as
a light source. A successful patterning of a 4 inch silicon wafer
with structures smaller than 50 nm was accomplished by such a
step-and-repeat method.
[0015] In an article entitled "Large-area patterning of 50 nm
structures on flexible substrates using near-field 193 nm
radiation", JVST B 21 (2002), at pages 78-81, Kunz et al. applied
near-field phase shift mask lithography to the nanopatterning of
flexible sheets (Polyimide films) using rigid fused silica masks
and deep UV wavelength exposure. In a subsequent article entitled
"Experimental and computational studies of phase shift lithography
with binary elastomeric masks", JVST B 24(2) (2006) at pages
828-835, Maria et al. present experimental and computational
studies of a phase shifting photolithographic technique that uses
binary elastomeric phase masks in conformal contact with layers of
photoresist. The work incorporates optimized masks formed by
casting and curing prepolymers to the elastomer
poly(dimethylsiloxane) against anisotropically etched structures of
single crystal silicon on Si02/Si. The authors report on the
capability of using the PDMS phase mask to form resist features in
the overall geometry of the relief on the mask.
[0016] U.S. Pat. No. 6,753,131 to Rogers et al, issued Jun. 22,
2004, titled "Transparent Elastomeric, Contact-Mode
Photolithography Mask, Sensor, and Wavefront Engineering Element",
describes a contact-mode photolithography phase mask which includes
a diffracting surface having a plurality of indentations and
protrusions. The protrusions are brought into contact with a
surface of a positive photoresist, and the surface is exposed to
electromagnetic radiation through the phase mask. The phase shift
due to radiation passing through indentations as opposed to the
protrusions is essentially complete. Minima in intensity of
electromagnetic radiation are thereby produced at boundaries
between the indentations and protrusions. The elastomeric mask
conforms well to the surface of the photoresist, and following
development of the photoresist, features smaller than 100 nm can be
obtained. (Abstract) In one embodiment, reflective plates are used
exterior to the substrate and the contact mask, so radiation will
be bounced to a desired location at a shifted phase. In another
embodiment, the substrate may be shaped in a manner which causes a
deformation of the phase shifting mask, affecting the behavior of
the phase shifting mask during exposure.
[0017] Near Field Surface Plasmon Lithography (NFSPL) makes use of
near-field excitation to induce photochemical or photophysical
changes to produce nanostructures. The main near-field technique is
based on the local field enhancement around metal nanostructures
when illuminated at the surface plasmon resonance frequency.
Plasmon printing consists of the use of plasmon guided evanescent
waves through metallic nanostructures to produce photochemical and
photophysical changes in a layer below the metallic structure. In
particular, visible exposure (.lamda.=410 nm) of silver
nanoparticles in close proximity to a thin film of a g-line
photoresist (AZ-1813 available from AZ-Electronic Materials,
MicroChemicals GmbH, Ulm, Germany) can produce selectively exposed
areas with a diameter smaller than .lamda./20. W. Srituravanich et
al. in an article entitled "Plasmonic Nanolithography", Nanoletters
V4, N6 (2004), pp. 1085-1088, describes the use of near UV light
(.lamda.=230 nm-350 nm) to excite SPs on a metal substrate, to
enhance the transmission through subwavelength periodic apertures
with effectively shorter wavelengths compared to the excitation
light wavelength. A plasmonic mask designed for lithography in the
UV range is composed of an aluminum layer perforated with 2
dimensional periodic hole arrays and two surrounding dielectric
layers, one on each side. Aluminum is chosen since it can excite
the SPs in the UV range. Quartz is employed as the mask support
substrate, with a poly(methyl methacrylate) spacer layer which acts
as adhesive for the aluminum foil and as a dielectric between the
aluminum and the quartz. Poly(methyl methacrylate is used in
combination with quartz, because their transparency to UV light at
the exposure wavelength (i-line at 365 nm) and comparable
dielectric constants (2.18 and 2.30, quartz and PMMA,
respectively). A sub-100 nm dot array pattern on a 170 nm period
has been successfully generated using an exposure radiation of 365
nm wavelength. Apparently the total area of patterning was about 5
.mu.m.times.5 .mu.m, with no scalability issues discussed in the
paper.
[0018] Joseph Martin has suggested a proximity masking device for
Near-filed lithography in U.S. Pat. No. 5,928,815, where
cylindrical block covered with metal film for light internal
reflection is used for directing light to the one end of the
cylinder (base of the cylinder), which contains a surface relief
pattern used for Near-field exposure. This block is kept in some
proximity distance ("very small, but not zero") from the
photoresist on the sample. Cylinder is translated in horizontal
direction using some precise mechanism, which is used to pattern
photoresist area.
[0019] The only published idea about using rollers for optical
lithography can be found in the Japanese Unexamined Patent
Publication, No. 59200419A, published Nov. 13, 1984, titled "Large
Area Exposure Apparatus". Toshio Aoki et al. described the use of a
transparent cylindrical drum which can rotate and translate with an
internal light source and a film of patterned photomask material
attached on the outside of the cylindrical drum. A film of a
transparent heat reflective material is present on the inside of
the drum. A substrate with an aluminum film on its surface and a
photoresist overlying the aluminum film is contacted with the
patterned photomask on the drum surface and imaging light is passed
through the photomask to image the photoresist on the surface of
the aluminum film. The photoresist is subsequently developed, to
provide a patterned photoresist. The patterned photoresist is then
used as an etch mask for an aluminum film present on the
substrate.
[0020] There is no description regarding the kinds of materials
which were used as a photomask film or as a photoresist on the
surface of the aluminum film. A high pressure mercury lamp light
source (500 W) was used to image the photoresist overlying the
aluminum film. Glass substrates about 210 mm (8.3 in.).times.150 mm
(5.9 in.) and about 0.2 mm (0.008 in.) thick were produced using
the cylindrical drum pattern transfer apparatus. The feature size
of the pattern transferred using the technique was about 500 .mu.m,
which was apparently a square having a dimension of about 22.2
.mu.m.times.22.2 .mu.m. This feature size was based on the
approximate pixel size of an LCD display at the time the patent
application was filed in 1984. The photomask film on the outside of
the cylindrical drum was said to last for approximately 140,000
pattern transfers. The contact lithography scheme used by Toshio
Aoki et al. is not capable of producing sub-micron features.
[0021] It does not appear that nanoimprinting methods (thermal or
UV-cured) or soft lithography using printing with SAM materials are
highly manufacturable processes. In general, the imprinting method
creates deformation of the substrate material due to the thermal
treatment (thermal NIL, for example) or shrinkage of pattern
features upon polymer curing (UV-cured polymeric features).
Moreover, due to the application of pressure (hard contact) between
a stamp and a substrate, defects are essentially unavoidable, and a
stamp has a very limited lifetime. Soft lithography does have an
advantage in that it is thermal and stress-free printing
technology. However, the use of a SAM as an "ink" for a sub-100 nm
pattern is very problematic due to the drifting of molecules over
the surface, and application over large areas has not been proved
experimentally.
[0022] Earlier authors have suggested a method of nanopatterning
large areas of rigid and flexible substrate materials based on
near-field optical lithography described in Patent applications
WO2009094009 and US20090297989, where a rotatable cylindrical or
cone-shaped mask is used to image a radiation-sensitive material.
The nanopatterning technique makes use of Near-Field
photolithography, where the mask used to pattern the substrate is
in contact with the substrate. The Near-Field photolithography may
make use of an elastomeric phase-shifting mask, or may employ
surface plasmon technology, where a rotating cylinder surface
comprises metal nano holes or nanoparticles.
SUMMARY OF THE INVENTION
[0023] Embodiments of the invention pertain to methods and
apparatus useful in the nanopatterning of large area substrates,
rigid flat or curved objects or flexible films. The nanopatterning
technique makes use of Near-Field UV photolithography, where the
mask used to pattern the substrate is in contact with the
substrate. The Near-Field photolithography may include a
phase-shifting mask or surface plasmon technology. The Near-field
mask is fabricated from a flexible film, which is nano structured
in accordance with the desired pattern. In phase-shift method, one
can use nanostructured elastomeric film, for example,
Polydimethylsiloxane (PDMS) film. Nanostructuring can be done using
laser treatment, selective etching or other available techniques,
or it can be done by replication (molding, casting) from the
nanostructured "masters", which are fabricated using known
nanofabrication methods (like, e-beam writing, holographic
lithography, direct laser writing or Nanoimprint step-and-repeat or
roll-to-roll lithography). This film can be supported by another
transparent flexible film (carrier). In plasmonic method one can
use a film with metal layer having nanohole structure, created
using one of the abovementioned methods or by depositing metal
nanoparticles, for example, deposited from a colloid solution. In
order to provide uniform contact area for near-field lithography we
rely on Van-der-Vaals forces of stiction between elastomeric film
and photoresist layer on the substrate. Alternatively, a
transparent cylinder is used to provide controllable contact
between nanostructured film and a substrate. Such cylinder may have
flexible walls and can be pressurized by a gas to provide
controllable pressure between a nanostructured film and a
substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] So that the manner in which the exemplary embodiments of the
present invention are attained is clear and can be understood in
detail, with reference to the particular description provided
above, and with reference to the detailed description of exemplary
embodiments, applicants have provided illustrating drawings. It is
to be appreciated that drawings are provided only when necessary to
understand exemplary embodiments of the invention and that certain
well known processes and apparatus are not illustrated herein in
order not to obscure the inventive nature of the subject matter of
the disclosure.
[0025] FIG. 1A shows a cross-sectional view of an embodiment of a
flexible nanostructured film 1, having a phase-shift mask
properties. Surface relief nanostructure 3 is fabricated on one of
the surfaces of the film 2.
[0026] FIG. 1B shows a cross-sectional view of an embodiment of a
flexible nanostructured film 1, having a plasmonic mask properties.
An array of nanoholes is created in the film or array of
nanoparticles are deposited on its surface.
[0027] FIG. 2 shows a suggested nanopatterning system prior to
starting the process. A nanostructured film 1 is wrapped around
support drums 4 and 5. Substrate 6 has a photoresist layer 7
deposited on its surface.
[0028] FIG. 3 shows another embodiment where nanostructured film 1
can be rolled from one roll 4 to another roll 5.
[0029] FIG. 4 shows a starting point of the process, when a film 1
is brought to contact with a photoresist 7 using movable arm 8.
[0030] FIG. 5 shows the patterning process, when the arm 8 is
removed from the film-substrate contact, substrate 6 is translating
in one direction, and UV light source 7 is illuminating the contact
zone between a film and a substrate.
[0031] FIG. 6 shows another embodiment, where a nanopatterned film
is in contact with the substrate in a quite wide surface area.
[0032] FIG. 7 shows an embodiment, where the transparent cylinder
11 is used to bring nanostructured film 1 in contact with
photoresist 7 on the substrate 6.
[0033] FIG. 8 shows an embodiment, where the substrate is a
flexible film 12, which can be translated from one roll 14 to
another 13.
[0034] FIG. 9 shows the embodiment, where the substrate is
nanopatterned from the both sides.
[0035] FIG. 10a and FIG. 10b illustrate alternative embodiments
involving patterning of non-flat or curved substrates.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0036] As a preface to the detailed description, it should be noted
that, as used in this specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents,
unless the context clearly dictates otherwise.
[0037] When the word "about" is used herein, this is intended to
mean that the nominal value presented is precise within +-10%.
[0038] Embodiments of the invention relate to methods and apparatus
useful in the nanopatterning of large area substrates, where a
flexible nanostructured film is used to image a radiation-sensitive
material. The nanopatterning technique makes use of near-field
photolithography, where the wavelength of radiation used to image a
radiation-sensitive layer on a substrate is 650 nm or less, and
where the mask used to pattern the substrate is in contact with the
substrate. The near-field photolithography may make use of a
phase-shifting mask, or may employ surface plasmon technology,
where a metal layer on movable flexible film's surface comprises
nano holes, or metal nanoparticles are dispersed on the surface of
such flexible film. The detailed description provided below is just
a sampling of the possibilities which will be recognized by one
skilled in the art upon reading the disclosure herein.
[0039] One of the embodiments suggests a phase-shift mask approach
and is implemented by flexible nanostructured film. The problem of
providing a uniform and permanent contact between such flexible
nanostructured film and a substrate is solved by manufacturing this
film from a material capable of creating strong but temporary bond
to photoresist layer. One example of such material is an elastomer,
for example Polydimethylsiloxane (PDMS). A PDMS film can be used to
form a conformal, atomic scale contact with a flat, solid layer of
photoresist. This contact is established spontaneously upon
contact, without applied pressure. Schematic of such film is shown
on FIG. 1A, where film 2 has a nanostructure 3 in the form of
transparent surface relief.
[0040] Film 2 can be made from one material (for example, PDMS) or
be a composite or multi-layer comprised of more than one material,
for example, nanostructured PDMS can be laminated or deposited on a
transparent and flexible support film. Such support film can be
made of polycarbonate (PC), polymethylmethacrylate (PMMA),
Polyethylene terephthalate (PET), amorphous fluoric-polymer, for
example CYTOP, and other materials. Deposition of PDMS on
transparent flexible support film can be done using one of
available techniques, for example, dipping, spraying or casting.
Support film can be treated using oxygen plasma, UV ozone, corona
discharge or adhesion promoters, like silanes to promote better
adhesion between elastomeric film and a polymer film support.
[0041] Another embodiment of "sticky" material, which can be used
instead of elastomer, to create a dynamic contact with photoresist
is cross-linked silane material. Such material can be deposited
from a silane precursor (usually used to deposit self-assembled
monolayers, SAMs) with abundance of water/moisture. For example,
DDMS (dichlorodimethylsilane) creates very sticky surface if
deposited with abundance of moisture. In this embodiment, the
carrier layer is nanostructured using one of known nanostructuring
techniques (preferably, Roll-to-Roll Nanoimprint lithography) and
then coated with silane material to provide "stickyness".
[0042] A surface relief for phase-shift lithography can be created
in the elastomeric or silane film using any of the following
methods: First, nanostructured "master" can be obtained using one
of the available nanofabrication techniques (deep-UV stepper,
e-beam, ion-beam, holography, laser treatment, embossing,
Nanoimprint, and others). Second, a replica of desired
nanostructure can be obtained from such master on the surface of
elastomeric film using, for example, casting or molding, in
roll-to-roll or step-and-repeat mode.
[0043] Another embodiment suggests that the carrier layer may be
nanostructured using a suitable nanostructuring technique (e.g.,
Roll-to-Roll Nanoimprint lithography with a UV-curable liquid
resist) and then coated with elastomer material (like PDMS) or
silane material (like DDMS) to provide "stickyness".
[0044] The nanostructure of such a mask can be designed to act as
phase shifter, and in this case the height of the features should
be proportional to .pi.. For example, PDMS material having
refractive index 1.43 for wavelength of exposure 365 nm should have
features with depth about 400 nm to cause a phase shift effect. In
this case a local minima of light intensity will happen at the step
edges of the mask. For example, lines from 20 nm to 150 nm can be
obtained in photoresist corresponding to the positions of surface
relief edges in the phase-shift mask. Thus this lithography has
image reduction properties, and nanostructures can be achieved
using much larger features on the mask.
[0045] Another embodiment is using nanostructure on flexible mask
to act as 1:1 replication mask. As it was demonstrated in previous
publications, for example, Tae-Woo Lee, at al in Advanced
Functional Materials, 2005, 15, 1435., depending on specific
parameters of photoresist exposure and development, one can achieve
1:1 replication of the features from mask to photoresist or feature
size reduction using phase-shift on the surface relief edges on the
same elastomeric mask. Specifically, underexposure or
underdevelopment against the normal exposure doze and development
time, would cause a significant differential between an effective
exposure doze in non-contact and contact regions of the mask. This
can be used to create a 1:1 replication from mask to photoresist in
positive or negative tone (depending on photoresist type).
Alternatively, the flexible mask 1 may be used with a UV-curable
liquid resist 7 to pattern the substrate 6, e.g., in Rolling Mask
imprint lithography.
[0046] Another embodiment suggests a plasmonic mask approach. Such
plasmonic film could be a flexible metal film, shown on FIG. 1B,
which has arrays of nanoholes according to the desired pattern.
Alternatively, metal layer is deposited on flexible transparent
film. Metal layer patterning can be done using one of available
nanopatterning techniques (deep-UV stepper, e-beam, ion-beam,
holography, laser treatment, embossing, Nanoimprint, and others),
followed by metal layer etching.
[0047] Alternatively, a nanopattern can be fabricated using
abovementioned methods on a transparent film, and then metal
material can be deposited over nanopatterned resist, followed by
metal layer lift-off.
[0048] And yet another embodiment uses metal nanoparticles
dispensed in controllable way over the surface of the flexible
transparent film to create a plasmonic mask. For example, metal
nanoparticles can be mixed with PDMS material in a liquid phase
prior to depositing it onto the flexible transparent support film.
Alternatively, metal nanoparticles can be deposited onto
nanotemplate fabricated in elastomeric layer.
[0049] A nanostructured film can be wrapped around support drums 4
and 5, and kept at a controllable tension, as shown on FIG. 2.
[0050] Alternatively, a nanostructured films can be rolled from one
roll 4 to another roll 5, as shown on FIG. 3.
[0051] The process starts by bringing a nanostructured film 1 in
contact with the photoresist 7 deposited on the substrate 6, using
a movable arm 8, as shown on FIG. 4. Such contact will engage
Van-der-Vaals forces and make film temporary stick to the
photoresist. Then, as it is shown on FIG. 5, movable arm 8 is
removed from the film-substrate contact, light source, which may
include optical focusing, collimating or filtering system, 9 is
turned on, providing exposure to the area of film-substrate
contact, and substrate 6 is translated in one direction using
constant or variable speed. Such translation will make film to move
as well in the direction of the translation, exposing different
parts of the substrate to the same or different pattern, depending
on the nanostructure fabricated on the film.
[0052] Another embodiment, presented in FIG. 6, shows
nanostructured film in contact with the photoresist across a wider
area. This area of contact starts to move as soon as substrate
begins translation in one direction. The width of contact area
between a nanostructured film and a substrate can be changed by
changing a relative position between the substrate 6 and drums 4
and 5, and also by changing tackiness of the nanostructured film
material. This configuration also allows an increase in the area of
the nanostructured film that is exposed to light, which helps to
improve a throughput of the method due to increase in dynamic
exposure dosage.
[0053] When nanostructured film surface contact is not tacky enough
(like, for example, in case of plasmonic mask approach) the movable
arm is not retracted, keeping controllable and uniform pressure
between the nanostructured film and a substrate. For example, the
movable arm can be fabricated in the form of transparent cylinder 1
1, as shown on FIG. 7. This cylinder is actuated by the mechanical
system providing controllable and uniform contact between
nanostructured film and a substrate. In that case, source of
illumination 9 could be located inside such a cylinder.
[0054] Such cylinder can be made from transparent flexible material
and pressurized by a gas. In such case the area of contact and
pressure between a mask and a substrate can be controlled by gas
pressure.
[0055] The gas can be flown through flexible-wall cylinder
constantly such as to create necessary controllable pressure and at
the same time cool down the light source positioned inside this
cylinder.
[0056] Disclosed nanopatterning methods can be used to pattern
flexible films 12, as shown on FIG. 8, which can be translated from
one roll 14 to another roll 13 during exposure.
[0057] Disclosed nanopatterning methods can be used to pattern
rigid or flexible materials from the both sides, as shown on FIG.
9.
[0058] Disclosed nanopatterning methods can be used to pattern
non-flat or curved substrates, as shown on FIG. 10. FIG. 10a shows
how cylinder 101 on a movable arm 103 is following the curvature of
the substrate 105, and FIG. 10b shows how flexible-wall gas
pressurized cylinder 111 is following the curvature of the
substrate 115. In the latter case, instead of moving the arm in the
vertical direction, one can adjust pressure inside cylinder 111 to
accommodate substrate height deviation caused by curvature.
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